The present application relates to lift cranes, and particularly to mobile lift cranes having a counterweight that can be moved to different positions in an effort to balance a load on the crane.
Lift cranes typically include counterweights to help balance the crane when the crane lifts a load. Since the load is often moved in and out with respect to the center of rotation of the crane, and thus generates different moments throughout a crane pick, move and set operation, it is advantageous if the counterweight, including any extra counterweight attachments, can also be moved forward and backward with respect to the center of rotation of the crane. In this way a smaller amount of counterweight can be utilized than would be necessary if the counterweight had to be kept at a fixed distance.
However, when there is no load on the hook, it is necessary to make sure that the counterweight is not in position to tip the crane backwards. Thus, if the crane needs to move without a load on the hook, the extra counterweight attachment must be close enough to the body. Additionally, safety codes may limit the distance and amount of counterweight used to prevent tipping in the case of loss of load. Thus for maximum lifting capacity, the counterweight may be extended as far as possibly while complying with general safety concerns and safety regulations which limit the extent that a counter weight may be extended from the crane.
Current systems generally position the counterweight as far away from the crane body as possible for a given boom configuration, while maintaining compliance with safety regulations or other concerns. With the counterweights in this position, the crane is at its maximum lifting capacity for the amount of counterweights present. Based on maximizing capacity alone, there is no reason why the counterweight would ever need to be positioned less than the maximum allowable extension.